DRAKE'S EQUATION

Drake's equation provides a way to quanitatively estimate the number of
civilizations present in our Galaxy that are are technically able to
communicate.

N = R*fp*ne*fl*fi*fc*L

N =
The number of communicating civilizations is the product of the following:

R =
The star formation rate in our galaxy: the number of new stars formed
per year. **

fp = The fraction of stars with planets around them.

ne = The number of habitable planets per star system.

fl = The fraction of habitable planets that develop life.

fi = The fraction of living planets that develop
intelligent life.

fc = The fraction of intelligent species that develop
technology capable of communicating across space (e.g., radio broadcasts).***

L = The lifetime a civilization spends in the technological
broadcast phase.

** We might wish to restrict this to solar type stars or otherwise consider
only "suitable" stars.

*** This implies a willingness to make the effort to use technology to
communicate. We've been broadcasting I Love Lucy for decades,
but the signal will quickly fade thanks to the inverse square law.
Even if another species can detect this broadcast from many light-years
away, would this constitute a recognizable attempt at intelligent
communication?